Field of the Invention
This invention relates to color cathode ray picture tubes, and is addressed specifically to the manufacture of tubes having shadow masks of the tension foil type in association with a substantially flat faceplate. The invention is useful in the manufacture of color tubes of various types, including those used in home entertainment television receivers, and in medium-resolution and high-resolution tubes intended for color monitors.
The tension foil shadow mask is a part of the cathode ray tube front assembly, and is located in close adjacency to the faceplate. As used herein, the term "shadow mask" means an apertured metallic foil which may, by way of example, be about 0.001 inch thick, or less. The mask is supported in high tension a predetermined, precise distance from the inner surface of the faceplate known as the "Q-distance."
As is well known in the art, the shadow mask acts as a color-selection electrode, or "parallax barrier," which ensures that each of the three beams generated by the electron gun located in the neck of the tube lands only on its assigned phosphor deposits.
The requirements for a support means for a foil shadow mask are stringent. As has been noted, the foil shadow mask is normally mounted under high tension, typically 30 lb/inch. The support means must be of high strength so the mask is held immovable; an inward movement of the mask of as little as 0.0002 inch can cause the loss of guard band. Also, it is desirable that the shadow mask support means be of such configuration and material composition as to be compatible with the means to which it is attached. As an example, if the support means is attached to glass, such as the glass of the inner surface of the faceplate, the support means must have a coefficient of thermal expansion compatible with the glass, and by its composition, be bondable to glass. Also, the support means should be of such composition and structure that the mask can be secured to it by production-worthy techniques such as electrical resistance welding or laser welding. Further, it is essential that the support means provide a suitable surface for mounting and securing the mask. The material of which the surface is composed should be adaptable to machining or other forms of shaping so that it can be contoured into near-perfect flatness so that no voids between the metal of the mask and the support structure can exist to prevent the positive, all-over contact required for proper mask securement.
Tension mask support structures have comprised a metal alloy cemented directly to the glass of the faceplate; examples of this type of assembly include, among others of common ownership herewith, those fully described and claimed in referent copending application Ser. Nos. 178,175 and 269,822. Tension mask support structures have also comprised ceramics cemented to the glass of the faceplate; examples of this type of assembly include, among others of common ownership herewith, those fully described and claimed in U.S. Pat. No. 4,737,681 and referent copending applications Ser. Nos. 269,822, 292,197 and 366,478. Further, the ceramic mask support may be discontinuous or "segmented," as described and claimed in referent copending application Ser. No. 421,909, a pending reissue of U.S. Pat. No. 4,730,143, also of common ownership herewith, and in referent copending application Ser. No. 427,149.
To forestall cracking or spalling of the glass of the the support structure to the glass of the faceplate, it is essential that the coefficients of thermal contraction ("CTC") of the glass of the faceplate, the metal used in a tension mask support structure, and the devitrifying solder glass (known coloquially as "frit"), used for cementing the structure to the faceplate, be compatible.
Significant factors in the manufacture of a tension mask support structure include: (1) the cost of the materials of the structure; (2) the compatibility of the composition of the support structure with the glass of the faceplate; (3) the flatness/parallelism of the structure; and most important, (4), the exactness and regularity of the Q-height.
Machining operations such as grinding or lapping e.g. have in the past provided for establishing exactness and regularity of Q-height of a support structure for a flat tension mask. A process for grinding a support structure to a desired Q-height is set forth in referent copending application Ser. No. 140,464, of common ownership herewith.
Other Prior Art
U.S. Pat. Nos. 3,894,321 to Moore; 4,695,761 to Fendley; and 4,828,523 to Fendley et al.